Levers

Description

This is a basic physics GCSE tutorial examining the turning effect of levers.

What are turning levers?

In general terms, a lever is a tool that makes work easier to do. By 'easier', we mean that levers reduce the amount of effort required to do the same amount of work. The best way to get your head around this is to go through an example.

To move a box weighing 400 N up a vertical distance of 0.5 metres requires 200 joules of energy. We know this is the case by working out the work required using the formula below.

Work = force x distance
W = f x s
W = 400 N x 0.5 m
W = 200 J

In this example, we can say that the force required to lift the box is 400 N. We can call this the load force. The effort force is the force required to do the work of lifting. Without a lever, the effort force is the same as the load force. The purpose of the lever is to reduce the effort force.

What if we add a lever?

The load force will remain the same, however a lever will reduce the effort force; let's see how. In this example balancing the moments on either side to make the lever horizontal will lift the box the desired 0.5 m vertically from its starting point.

Using the technique we learned in the previous tutorial, let's work out what force would need to be exerted on the right hand side for the moments (and thus the lever) to balance.

As you can see, using a lever will reduce the effort force from 400 N to 160 N.

While the effort force has reduced, the work will still be the same. How does that happen? Although the effort force has reduced (from 400 N to 160 N), the distance it needs to be applied across has actually increased (from 0.5 m to 1.25 m).

So in other words, the lever has reduced the effort force, but you need to apply it over a greater distance to achieve the same outcome as you would without the lever. You can discuss this in terms of a lever's mechanical and velocity ratios. But before we go through what those are, let's have a brief look at different types of levers.